Aviation and fuel consumption

Summary: Aviation fuel consumption in the United States reached a total of 18.2 billion gallons by airlines in 2019. Volatility in fuel prices, scarcity, and increasing environmental concerns are moving the sector toward the use of alternative fuels.

Flying has been a constant goal for humankind; evidence of the human ambition to fly can be found in the imagery, mythology, arts, literature, and science of all civilizations. For centuries, different types of inventions—ornithopters, gliders, kites, and other flying devices—were envisioned; most of them were human-powered machines emulating movements and principles from nature.

Pioneering attempts in aviation considered thermal energy for lifting purposes, including the Montgolfier brothers’ hot-air balloon in 1783 and Count von Zeppelin’s airship, which performed its first flight in 1900. Aviators experimented with steam engines in the last quarter of the nineteenth century, but with limited success. More significant developments occurred early in the twentieth century, when Wilbur and Orville Wright designed and operated the world’s first heavier-than-air powered airplane at Kitty Hawk, North Carolina, in 1903. In the summer of 1919, the first nonstop transatlantic flight took place, piloted by the British war pilots John Alcock and Arthur W. Brown. These first flights used shaft-based engines fueled by gasoline. Military aviation served as a testing ground for both engines and fuel, and during this time the propeller-driven piston engine, operating on aviation gasoline (Avgas), was perfected. Avgas, with an octane rating of 100, replaced the lower-octane fuel of standard gasoline, which also had a dangerous flashpoint (lower than 1 degree Celsius).

However, the invention of the jet engine, in the 1940s, is regarded as the key milestone in aviation history. It enabled faster flights and greatly enhanced aircraft capacity. In the 1950s, the British Overseas Airways Corporation (BOAC) led the jet age of commercial aviation, with civil transport of freight and passengers. Energy consumed by commercial aviation since then has mostly been a kerosene-based fuel, and the use of Avgas 1001L became residual. Jet A1 is now the most commonly used civil jet fuel, followed by Jet A, which is sold only in the United States, and Jet B. Military aviation can use other fuels, such as JP4, JP5, and JP8. Aviation fuels are characterized by a high energy density and are required to meet stringent and internationally accepted specifications.

In the early years, the vertiginous expansion of aviation prompted international concerns over the need for regulation of this new activity. In 1944, the Convention on International Civil Aviation was signed in Chicago, leading to the creation of the International Civil Aviation Organization (ICAO), an agency of the United Nations and the natural forum for the international community to set rules and to facilitate understanding and cooperation for a homogeneous and consistent legal framework for aviation. ICAO developed a body of regulations, recommendations, and standards to promote security, safety, and air traffic. Later, environmental issues became part of the organization’s agenda, including goals related to fuel efficiency and alternative fuels.

Aviation energy demand has steeply increased in the last century, reflecting the globalization process, the democratization of air transport, and the difficulty in substituting other means of transportation for air travel. The Intergovernmental Panel on Climate Change in its special report Aviation and the Global Atmosphere (released in 1999), showed how, in future growth scenarios, improvements in fuel efficiency would be undermined by high levels of sustained energy demand in the sector, with an annual average increase of 3 percent between 1990 and 2015.

Since 1970, aircraft fuel efficiency has increased by 70 percent, running at an annual average rate of 4.5 percent until it dropped to 1.2 percent at the beginning of the twenty-first century. In addition to this drop-off in efficiency improvements, growth in demand means that absolute levels of energy consumption in the global aviation industry are on the increase. Air travel demand, measured by revenue per passenger kilometer, increased 6.3 percent per year between 1972 and 2007. The ICAO’s environmental report for 2007 states that almost 4 trillion passenger-kilometers were registered in 2006 and that international passenger traffic was expected to increase an annual rate of 5.3 percent for the period 2005–25. This trend was thwarted by the global COVID-19 pandemic, which saw most travel come to a standstill in 2020. With emerging economies joining the Western model of lifestyle and the boost of trade activities between Asia, the United States, and Europe, energy demand from the aviation sector is due to continue, whereas in other sectors it is expected to decline. In China, demand for aviation has grown an average rate of 14.8 percent per year since the 1990s.

The world’s leading aircraft manufacturers include the American company Boeing and the European corporation Airbus (founded in 1967 to promote economic and technological progress in European aviation). Both increased their sales in 2010 even in the context of a world economic crisis and were fiercely competitive for their share in the market since the 1990s. Airbus delivered its first plane in 1974 and reached 10,000 orders in January 2011, slightly overtaking its competitor. By 2023, Boeing was on top with revenue of $66.6 billion followed by American manufacturer Lockheed Martin ($65.9 billion). Airbus had fallen to third place with $61.7 billion in revenue.

Aircraft Fuel Cost and Efficiency

As a pioneering sector for technology, aircraft design and engines are constantly improving to perform more efficiently, and operational measures are revised to reduce fuel consumption and environmental impact. Fuel efficiency is achieved mainly by improvements in jet engines, although it is argued that the last piston engines had a better efficiency index than the first jet engines; other variables, such as airplane design, new materials, load factors, operational measures, airspace control, and airport measures, can also help to reduce fuel consumption. Aircraft such as the Airbus A380, the world’s largest passenger plane, use around three liters of fuel per 100 passenger kilometers. Airlines that operate more short-haul flights tend to record lower fuel efficiencies (measured in liters of fuel per passenger kilometer), because aircraft consume higher amounts of fuel during takeoff and landing. However, aviation is considered to be a mature technology, where opportunities for achieving significant new efficiencies are limited. A technological breakthrough in the short term is unlikely to happen, but some leading aeronautic institutions are looking at a 40-year framework for delivering aircraft designs that could save significant amounts of fuel compared with traditional ones.

The price of jet fuel is linked to the price of crude oil, and for the first few years of the twenty-first century it fluctuated around $40-$60 (US) per barrel. However, it soon began to climb. In 2008, when global oil prices reached an all-time high, US-based United Airlines claimed that it spent $173,000 to fuel a Boeing 747 for a single flight from Chicago to Hong Kong, the equivalent of $500 per seat. In 2010, a steeper increase took place, and for the next four years the price per barrel hovered between $120 and $140. In early 2015, however, fuel prices plunged, and returned to the $40 to $60 range. In 2023, crude oil averaged about $83 a barrel.

During the 1970s, the rise in fuel prices stimulated the industry to develop alternative fuels, and the 2008 fuel price spike forced some airlines into bankruptcy. However, it is important to note that the international airline industry is traditionally exempt from paying tax on jet fuel or, indeed, any environmental tax designed to internalize the external cost, such as taxes for carbon emissions.

The combustion of aviation fuel affects the environment through noise pollution, deterioration of local air quality, and a release of emissions into the atmosphere that contributes to climate change and ozone depletion. Globally, the aviation sector is responsible for 2.5 percent of anthropogenic carbon emissions, while its share in global warming in terms of radiative forcing is far higher, accounting for 3.5 percent in 1992 and predicted to be 5 percent by 2050. This significant rate results from the fact that most fuel emissions from aircraft occur in the troposphere, between 8 and 12 kilometers above sea level, where their impact on the environment is more intensive than those of land-based emissions. The main emissions from aircraft include carbon dioxide (CO₂), nitrogen oxides, water vapor, sulfur, and soot particles that also cause the formation of condensation trails (contrails) and the enhancement of cirrus clouds. Although CO₂ is the most abundant greenhouse gas emitted by aircraft engines, the Intergovernmental Panel on Climate Change (IPCC) estimates that non-CO₂ emissions, excluding the formation of cirrus clouds (over which there remain scientific uncertainties), are responsible for at least doubling the climate change impact of aviation.

In the European Union (EU), CO₂ emissions from aviation in the EU25 increased 73 percent between 1990 and 2004. During the same period, according to Eurostat, energy consumed by air transport within the EU rose by 67 percent. Tackling aviation greenhouse gas emissions is a priority for the EU. Although fuel burned per passenger decreased by 24 percent between 2005 and 2017, air traffic increased during the same time and more than offset the improvement.

Alternative Aircraft Fuel

The use of alternative energy to replace or supplement conventional jet fuel can help overcome the major environmental challenges faced by the sector, while limiting the dependence on already scarce and expensive petroleum-based fuels. The future of aviation energy is envisioned to follow the development of low-carbon fuels or even emissions-free hydrogen technology, and the scientific community, industry, and governments are already moving forward to develop alternative fuels. These fuels need to have a high energy intensity per unit of weight and volume, and their feasibility depends on their ability to be drop-in fuels, which do not require modifications in current engines and/or which can be blended with traditional jet fuels. The use of synthetic jet fuel derived from Fischer-Tropsch conversion from coal, natural gas, or biomass to liquid hydrocarbons is available typically in a 50 percent blend. This synthetic kerosene can also have a mineral origin but has some environmental and supply advantages when compared with traditional jet fuel. It is hoped that biofuels for aviation will be a viable option in the medium term. These include fermented jet fuel from sugars; hydro-treated renewable fuel produced from algae, jatropha, and camelina crops; and high energy raw materials from second-generation biofuels, which have superior sustainability and life-cycle benefits compared to other biofuels.

Sustainable aviation fuel (SAF) has been made using feedstocks and blended between 10 and 50 percent with aviation fuel. Hundreds of thousands of commercial flights at airports in the United States and Europe have used SAF.

Sustainable energy for aviation might include other sources, although scientific uncertainties remain high. Such is the case with hydrogen fuel technologies, which present weight and volume incompatibilities with air transport. Other renewable energy options for aviation are been tried and tested, including solar-powered aircraft. For example, Solar Impulse, a fixed-wing solar-powered aircraft, set a world record of more than 26 hours of continuous flight under solar power alone, including flight during more than nine hours of darkness.

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